Many wireless communication systems use base stations (communication stations, transceiver stations, eNodeBs, eNBs) to provide geographical service areas where wireless communication user equipment devices (UE devices) communicate with the base station providing the particular geographical service area in which the UE devices are located. The base stations are connected within a network allowing communication links to be made between the UE devices and other devices. The communication system may include base stations that provide overlapping service areas of different sizes to serve various needs of mobile UE devices. For example, macrocell communications stations may provide macrocell service areas that are larger and may cover one or more small cell service areas provided by small cell base stations.
In some circumstances, the communication links are between wireless communication UE devices that are close to each other. In these situations, it may be preferred to have a direct communication link between the two wireless UE devices rather than communicating through a base station. Such direct communication between devices is often referred to as device-to-device (D2D) communication or peer-to-peer (P2P) communication. The communication resources (e.g., time frequency blocks) used for D2D communication are typically a subset of the communication resources used by the communication system for communication between UE devices and the base stations.
An in-coverage (InC) UE device is a UE device that is within the service area of a base station and is capable of communication with the base station. An out-of-coverage (OoC) UE device is a UE device that is not within a service area of any base station. D2D UE devices that are engaged in D2D communication with each other form a group. A D2D group, therefore, includes two or more D2D UE devices. There are five typical coverage scenarios that occur with D2D groups. In a first coverage scenario, all the UE devices of the D2D group are located in a service area of a single base station. For the first scenario, therefore, all of the D2D UE devices of the D2D group are InC UE devices in a single service area. In a second coverage scenario, none of the UE devices of the D2D group are located inside any service area of any base station. For the second scenario, therefore, all of the D2D UE devices of the D2D group are InC UE devices. In a third coverage scenario, at least one of the UE devices of the D2D group is located in a service area of a single base station and at least one D2D UE device of the group is outside all service areas. For the third scenario, therefore, at least one of the D2D UE devices of the D2D group is InC UE device in a single service area and at least one UE device is an OoC UE device. The third coverage scenario is sometimes referred to as a partial coverage scenario. In a fourth coverage scenario, at least one of the UE devices of the D2D group is located within a first service area of a first base station and at least one D2D UE device of the group located within a second service area of a second base station. For the fourth scenario, therefore, at least two of the D2D UE devices of the D2D group are InC UE devices in different service areas. In a fifth coverage scenario, at least one of the UE devices of the D2D group is located within a first service area of a first base station, at least one D2D UE device of the group located within a second service area of a second base station, and at least one UE device of the D2D group is an OoC UE device. For the fifth scenario, therefore, at least two of the D2D UE devices of the D2D group are InC UE devices in different service areas and at least one D2D UE device of the group is an OoC UE device. Other coverage scenarios are possible. For the fourth and fifth coverage scenarios at least one UE device is served by one base station and at least one UE device is served by another base station. Such scenarios are typically referred to as an inter-cell coverage scenario. Since the UE devices of a group are mobile, there are situations where the coverage scenario of a D2D group changes. For example, a UE device of a D2D group may move from a first service area served by a first base station to a second service area served by a second base station.